1. Field of the Invention
The present invention relates to a touch sensing substrate and a touch sensing liquid crystal display (LCD). More particularly, the present invention relates to a low noise touch sensing substrate and a low noise touch sensing LCD.
2. Description of Related Art
Based on different sensing types, a touch sensing panel can be generally categorized into a resistive touch sensing panel, a capacitive touch sensing panel, an optical touch sensing panel, an acoustic-wave touch sensing panel, and an electromagnetic touch sensing panel. The capacitive touch sensing panel is characterized by short response speed, favorable reliability, satisfactory durability, and so on. Therefore, the capacitive touch sensing panel is just slightly less popular than the resistive touch sensing panel. According to structural and manufacturing differences, the capacitive touch sensing panel can be further classified into an added type touch sensing panel and an integrated/in-cell touch sensing panel. In the added type capacitive touch sensing panel, sensing series are first formed on a substrate, and the substrate having the sensing series is then adhered to an outer surface of a display. Apparently, the substrate of the added type touch sensing panel brings about an increase in entire thickness of the added type touch sensing panel, which is unfavorable to miniaturization and microminiaturization of the display.
FIG. 1A is a schematic view of a conventional touch sensing substrate. Referring to FIG. 1A, the conventional touch sensing substrate 100a includes a substrate 110, a plurality of X sensing series 120, a plurality of Y sensing series 130, a first dielectric layer 140, a second dielectric layer 150, and a common electrode 160. Each of the X sensing series 120 is electrically insulated from each other, and so is each of the Y sensing series 130. The first dielectric layer 140 covers the X sensing series 120 and the Y sensing series 130, and the first dielectric layer 140 is disposed at one side of the substrate 110. The second dielectric layer 150 and the first dielectric layer 140 are respectively located at opposite sides of the substrate 110. Besides, the second dielectric layer 150 and the first dielectric layer 140 include a plurality of color filter patterns 152, respectively. In addition, the common electrode 160 is disposed on the second dielectric layer 150.
As indicated in FIG. 1A, a parasitical capacitance CP of the conventional touch sensing substrate 100a includes a parasitical capacitance CX-Y generated between the X sensing series 120 and the Y sensing series 130 and a parasitical capacitance CX-COM generated between the X sensing series 120 and the common electrode 160. In other words, CP=CX-Y+CX-COM. Nonetheless, due to the thickness of the substrate 110, the value of the parasitical capacitance CX-COM appears to be rather small and can be neglected in comparison with the parasitical capacitance CX-Y. Therefore, CP(100a)≈CX-Y.
FIG. 1B is a schematic view of a conventional integrated touch sensing substrate. Referring to FIG. 1B, the conventional integrated touch sensing substrate 100b includes a substrate 110, a plurality of X sensing series 120, a plurality of Y sensing series 130, a first dielectric layer 140, a second dielectric layer 150, and a common electrode 160. The touch sensing substrate 100b has a similar structure to that of the touch sensing substrate 100a, while the main difference therebetween lies in that the X sensing series 120, the Y sensing series 130, the first dielectric layer 140, the second dielectric layer 150, and the common electrode 160 of the touch sensing substrate 100b are all disposed at the same side of the substrate 110. Additionally, a distance between the common electrode 160 and the X sensing series 120 and a distance between the common electrode 160 and the Y sensing series 130 are relatively short in the touch sensing substrate 100b in comparison with the touch sensing substrate 100a. 
It can be observed from FIG. 1B the parasitical capacitance generated by the conventional touch sensing substrate 100b is the same as the parasitical capacitance generated by the touch sensing substrate 100a, i.e., CP(100b)=CX-Y+CX-COM. However, the distance between the X sensing series 120 and the common electrode 160 of the touch sensing substrate 100b is merely several micrometers (μm), and accordingly the parasitical capacitance generated therebetween cannot be disregarded.
FIG. 1C is an equivalent circuit diagram of a conventional touch sensing substrate after the touch sensing substrate is touched. Referring to FIG. 1C, a capacitance CX-f is generated between the X sensing series and fingers after said two conventional touch sensing substrates 100a and 100b are touched by the fingers. That is to say, the capacitance CX-f between the X sensing series and the fingers is the so-called touch sensing signal, while the other capacitances are regarded as noises. Hence, a signal to noise (S/N) ratio is CX-f/CP. Namely, the S/N ratio=CX-f/CX-Y+CX-COM. Specifically, the touch sensing substrate 100a has an S/N ratio S/N(100a)=CX-f/CX-Y, while the touch sensing substrate 100b has an S/N ratio S/N(100b)=CX-f/CX-Y+CX-COM.
Based on the above, even though the touch sensing substrate 100b can be miniaturized and has a simple and easy manufacturing process, the S/N ratio of the touch sensing substrate 100b is much higher than that of the touch sensing substrate 100a, which is likely to result in erroneous actions. As such, the design of the integrated capacitive touch sensing panel still requires further improvement.